Now here's a thought .....
By using BACK-TL2-F'x'-SL4-SL trigger, the 'F' modifier only refers to the BACK bet so, as we've determined, this could lead to an open BACK bet.
IF 2 - EXCEL worksheets (call one BACK & other LAY) are used with BA feeding-in the same market into each worksheet, on the BACK worksheet the trigger BACK-F'x' can be used. On the LAY worksheet would want a LAY trigger with an 'F', SL4 and SL modifier,
so would LAY-F'x'-SL4-SL work to produce an Auto Level Profit/Loss? Obviously both worksheets would be formula linked to each other so references from one can be used on the other.
Then if the LAY bet hasn't been triggered after 'x' seconds it's automatically cancelled and a trade-out LAY bet (I'd probably use LAYR) can then be triggered using whatever odds are available (within reason

) to produce Auto Level Profit/Loss, thereby avoiding the current problem I (and I think 'Os') have of BACK bets not being traded out.
In a nut shell, rather than using BACK-TL2-F'x'-SL4-SL on one worksheet I want to split the BACK & LAY actions that this trigger does, over the 2 worksheets, but giving the same result. I think I can sort out the issue of open BACK bets from there.